Rubber compositions

ABSTRACT

The present invention provides a diene rubber composition having excellent processability and being improved in both the balance between low rolling resistance and wet skid resistance, and strength properties. The composition according to the invention is a diene polymer rubber composition comprising (A) 100 parts by weight of a raw material rubber comprising (A-1) a diene rubbery polymer which is a conjugated diene rubbery polymer or a conjugated diene-styrene rubbery copolymer (1) containing a modified component in an amount exceeding 60 wt. %, which modified component is obtained by reacting an active end of the rubbery polymer with a polyfunctional compound having, in its molecule thereof, at least two epoxy groups, (2) having a molecular weight distribution Mw/Mn of 1.05 to 3.0, and (3) having a weight-average molecular weight of 100,000 to 2,000,000; and, based on 100 parts of the component (A), (B) 1 to 100 parts by weight of a rubber extension oil, (C) 25 to 100 parts by weight of reinforcing silica, and (D) 1.0 to 20 parts by weight in total of a vulcanizing agent and a vulcanizing accelerator.

This application is a divisional of co-pending application Ser. No.09/856,845, filed on Oct. 29, 2001 and for which priority is claimedunder 35 U.S.C. § 120. Application Ser. No. 09/856,845 is the nationalphase of PCT International Application No. PCT/JP00/06600 filed on Sep.26, 2000 under 35 U.S.C. § 371. The entire contents of each of theabove-identified applications are hereby incorporated by reference. Thisapplication also claims priority of Application Nos. JP 11-272070 and JP11-272090 both filed in Japan on Sep. 27, 1999 under 35 U.S.C. § 119.

TECHNICAL FILED

The present invention relates to a conjugated-diene-rubber-containingrubber composition which has improved processability even if containingsilica as a filler, and also has excellent hysteresis loss propertiesand strength properties. More specifically, the invention pertains to anovel conjugated diene polymer rubber composition available by adding,to a diene rubber which has acquired a specific structure and hasimproved affinity with silica by modifying a conjugated diene rubberypolymer having an active end with an epoxy polyfunctional compound, anoil, silica, a vulcanizing agent and a vulcanizing accelerator andkneading the mixture. The vulcanizate thereof is suitably used forapplications, mainly, tires for which a conjugated diene polymer rubbercomposition has conventionally been used.

BACKGROUND ART

In recent years, there has been a strong social demand for reducing theamount of a CO2 exhaust gas for resource saving, energy saving andenvironmental protection. In order to reduce the amount of a CO2 gasdischarged from automobiles, various countermeasures such as weightreduction of them or use of electric energy are under investigation. Asa common theme in automobiles, an improvement of fuel-cost-savingperformance by improving the rolling resistance of a tire is regarded tobe necessary. At the same time, automobiles are desired to have improvedsafety upon traveling. Such fuel-cost-saving performance and safety ofautomobiles are largely influenced by the performances of tires usedtherefor so that there is a strong demand for improving fuel-cost-savingperformance, traveling stability and durability of automobile tires.Such properties of tires depend on various factors including structureand raw materials used for them. In particular, the performances of arubber composition used for the tread part of a tire to be brought intocontact with a road surface largely affects the properties of a tiresuch as fuel-cost-saving performance safety and durability. Under suchsituations, technical improvements in a tire rubber composition are nowfrequently studied and proposed and some have already beenindustrialized.

A tire tread is requested to have, for example, a small hysteresis lossfor improving its fuel-cost-saving performance, have high wet skidresistance for improving its controlling stability and have excellentwear resistance for improving its durability. However, a reduction inhysteresis loss and high wet skid resistance are not attainedsimultaneously, which also applies to the relationship between wearresistance and wet skid resistance. It is difficult to satisfy all theabove-described demands for an automobile tire by improving only oneperformance and an improvement of their balance is important. Typicalmethods for improving a tire rubber composition is to improve rawmaterials to be employed. An improvement in the polymer structure of araw material rubber such as SBR or BR or improvement in the structure orcomposition of a reinforcing filler such as carbon black or silica,vulcanizing agent or plasticizer has now been carried out.

One of the most attractive techniques among them in recent years is touse silica as a reinforcing filler instead of conventionally employedcarbon black. The typical technique of it is proposed, for example, inU.S. Pat. No. 5,227,425 wherein the balance of a tread rubbercomposition between a fuel-cost-saving performance and wet skidresistance is improved by adding, to SBR of a specific structure, silicaas a reinforcing filler and kneading the mixture under specifiedconditions. A rubber composition using silica as a reinforcing fillerhowever involves some problems to be solved. For example, since silicahas low affinity with a rubber compared with the conventionally employedcarbon black, its dispersibility in the rubber is not always good andthis inferior dispersibility tends to cause insufficient wear resistanceand insufficient strength properties. It is therefore necessary toimprove the dispersibility of silica by kneading under particulartemperature conditions in the presence of a silane coupling agenttypified by bis-(triethoxysilylpropyl)-tetrasulfide and in addition,increasing a kneading frequency.

Under such situations, a method of modifying the end of a rubber with analkoxysilyl group and silica-containing rubber compositions preparedthereby are proposed in JP-B-62-227908, JP-B-8-53513, JP-B-8-53576 andJP-B-9-225324 with a view to improving the dispersibility of silica inthe rubber and reducing the amount of the silane coupling agent. Thepolymer modified by an alkoxysilyl group is available by reacting anactive end polymer, which has been obtained by anionic polymerization,with a specific alkoxysilane compound. Such a polymer is howeveraccompanied with the problems that the alkoxysilyl group of theresulting polymer tends to be condensed by water content, therebycausing a change in the viscosity of the polymer with the passage oftime and in spite of an improvement in the dispersibility of silica, theresulting rubber composition has not always good processability owing toan increase in its viscosity.

A silica-containing composition using an epoxydated polymer is proposedin JP-B-9-118785 and JP-B-9-221429. It is however accompanied with theproblems that it needs a special epoxidation step with hydrogen peroxideor peracid upon obtaining a modified polymer and in addition, it has notalways good processability.

In JP-B-7-330959, proposed is a tire tread composition using SBR of aspecial structure, which has been obtained by coupling with adiglycidylamino-containing polyfunctional compound, with a view toimproving processability in production steps, reducing rollingresistance and improving wet skid resistance. In this case,incorporation of carbon black in at least a predetermined amount isrequired in order to impart the composition with performances such asprocessability and wear resistance and to suppress radio frequencynoise. It is further disclosed that the molecular weight distribution ofthe polymer falls within a specific range, the styrene content and1,2-bond content, each within a specific range are preferred, and atleast one unreacted glycidyl group is preferably contained in themolecule.

An object of the present invention is to provide, in consideration ofsuch situations, a silica-containing diene rubber composition which hasexcellent processability even if a content of carbon black is small andis improved in both the balance between low rolling resistance and wetskid resistance and strength properties.

DISCLOSURE OF THE INVENTION

With a view to attaining the above-described object, the presentinventors have carried out an extensive investigation on the molecularstructure and modified structure of a diene polymer and a manufacturingprocess of it. As a result, it has been found that a rubbery polymercontaining a predetermined amount of a specific modified component hasexcellent performances, leading to the completion of the invention.

Described specifically, the object of the present invention is attainedby provision of the following diene rubber polymer compositions anddiene rubber polymer vulcanizates:

1. A diene polymer rubber composition comprising:

(A) 100 parts by weight of a raw material rubber comprising (A-1) adiene rubbery polymer which is a conjugated diene rubbery polymer or aconjugated diene-styrene rubbery copolymer, said diene rubbery polymer

-   -   (1) containing a modified component in an amount exceeding 60        wt. %, which modified component is obtained by reacting an        active end of the rubbery polymer with a polyfunctional compound        having, in its molecule thereof, at least two epoxy groups,    -   (2) having a molecular weight distribution Mw/Mn of 1.05 to 3.0,        and    -   (3) having a weight-average molecular weight of 100,000 to        2,000,000; and, based on 100 parts by weight of the component        (A),

(B) 1 to 100 parts by weight of a rubber extension oil;

(C) 25 to 100 parts by weight of reinforcing silica; and

(D) 1.0 to 20 parts by weight in total of a vulcanizing agent and avulcanizing accelerator.

2. The diene polymer rubber composition according to item 1 above,wherein the polyfunctional compound further has at least onenitrogen-containing group.

3. The diene polymer rubber composition according to item 1 above,wherein the polyfunctional compound is represented by the followingformula:

wherein R¹ and R² each independently represents a C₁₋₁₀ hydrocarbongroup or a C₁₋₁₀ hydrocarbon group having at least one group selectedfrom ethers and tertiary amines, R³ and R⁴ each independently representshydrogen, a C₁₋₂₀ hydrocarbon group or a C₁₋₂₀ hydrocarbon group havingat least one group selected from ethers and tertiary amines, R⁵represents a C₁₋₂₀ hydrocarbon group, a C₁₋₂₀ hydrocarbon group havingat least one group selected from ethers, tertiary amines, epoxy,carbonyl and halogens, and n stands for 1 to 6.

4. The diene polymer rubber composition according to item 3 above,wherein the polyfunctional compound has, in its molecule thereof, atleast one diglycidylamino group.

5. The diene polymer rubber composition according to item 1 above,wherein the content of the modified component of the component (A-1) hasbeen analyzed by chromatography.

6. The diene polymer rubber composition according to item 1 above,further containing 0.1 to 20 wt. %, based on the weight of the component(C), of (E) an organosilane coupling agent.

7. The diene polymer rubber composition according to item 1 above, whichfurther contains (F) 0.1 to 100 parts by weight of carbon black, thetotal amount of the components (C) and (E) being from 30 to 150 parts byweight.

8. The diene polymer rubber composition according to item 7 above,wherein the amount of the component (F) is 0.1 parts by weight orgreater but less than 25 parts by weight.

9. The diene polymer rubber composition according to item 1 above,wherein the component (A-1) has a molecular weight distribution Mw/Mn(2) of 1.05 or greater but less than 2.2.

10. The diene polymer rubber composition according to item 1 above,wherein the component (A) comprising 15 to 99 wt. % of the component(A-1) and 1 to 85 wt. % of component (A-2) which is a vulcanizablerubbery polymer other than the component (A-1).

11. R diene polymer rubber vulcanizate obtained by:

conducting initial kneading, at least once under the conditionspermitting kneading discharging temperature of 135 to 180° C., of aninitial kneading component comprising:

(A) 100 parts by weight of a raw material rubber comprising (A-1) adiene rubbery polymer which is a conjugated diene rubbery polymer or aconjugated diene-styrene rubbery copolymer, said diene rubbery polymer

-   -   (1) containing a modified component in an amount exceeding 60        wt. %, which modified component is obtained by reacting an        active end of the rubbery polymer with a polyfunctional compound        having, in its molecule thereof, at least two epoxy groups,    -   (2) havaing a molecular weight distribution of Mw/Mn of 1.05 to        3.0, and    -   (3) having a weight-average molecular weight of 100,000 to        2,000,000; and, based on 100 parts by weight of the component        (A),

(B) 1 to 100 parts by weight or a rubber extension oil; and

(C) 25 to 100 parts by weight of reinforcing silica, to thereby obtainan initial kneaded mass having a rubber bound content after kneading of30 to 70 wt. %;

adding, to 100 parts by weight of the component (A), (D) 1.0 to 20 partsby weight in total of a vulcanizing agent and a vulcanizing accelerator;and

kneading the resulting mixture to give a kneading dischargingtemperature of 120° C. or less, thereby vulcanizing.

12. The diene polymer rubber vulcanizate according to item 11 above,wherein the initial kneading component further contains at least one of0.1 to 20 wt. % of (E) an organosilane coupling agent based on theweight of the component (C) and 0.1 to 100 parts by weight of (F) carbonblack based on 100 parts by weight of the component (A).

13. The diene polymer rubber vulcanizate according to item 11 above,wherein the component (A) comprises 15 to 99 wt. % of the component(A-1) and (A-2) 1 to 85 wt. % of a vulcanizable rubbery polymer otherthan the component (A-1).

14. The diene polymer rubber vulcanizate according to item 12 above,wherein the amount of the component (E) is 0.1 wt. % or greater but lessthan 6 wt. % based on the amount of the component (C).

15. The diene polymer rubber vulcanizate according to item 11 above,wherein initial kneading is carried out to give the below-describedkneading discharging temperature (Td) depending on a heating loss (Mo)of the component (C).

1) 135≦Td≦180° C. when 1%≦Mo≦4%

2) (15×Mo+75)° C.<Td≦180° C. when 4%<Mo≦6% and

3) 165° C.<Td≦180° C. when 6%<Mo≦10%.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will hereinafter be described more specifically.

For the vulcanized rubber composition of the present invention, aspecific rubbery polymer (Component (A-1)) is used as a rubbery polymer.The specific rubbery polymer (Component (A-1)) of the invention is aspecific conjugated diene rubbery polymer or conjugated diene-styrenerubbery copolymer and it contains, in an amount exceeding 60 wt. %, amodified component obtained by reacting, in an inert solvent, anactive-end-having conjugated diene rubbery polymer or conjugateddiene-styrene rubbery copolymer available by anionic polymerization witha polyfunctional compound having, in the molecule thereof, at least twoepoxy groups.

In the present invention, preferred examples of the conjugated diene ofthe conjugated diene rubbery polymer or conjugated diene-styrene rubberycopolymer include 1,3-butadiene and isoprene. Styrene to becopolymerized is preferably a random copolymer. The “random copolymer”as used herein does not contain a component having a styrene chainlength of 30 or greater, or if any, contains it in a small amount.Described specifically, preferred is a random copolymer having such acomponent in an amount of 10 wt. % or less, preferably 5 wt. % or lessbased on the amount of the polymer as analyzed by a known method whereinthe polymer is decomposed by the Kolfthoff's method and the amount ofpolystyrene unnecessary for methanol is analyzed; or a random copolymercontaining a component whose styrene chain length is 8 or greater in anamount of 5 wt. % or less relative to the amount of the polymer asanalyzed by a known method wherein the polymer is decomposed by themethod employed for ozone decomposition and the styrene chaindistribution is analyzed by GPC. As needed, it may be copolymerized with10 wt. % or less of another copolymerizable monomer.

In this manufacturing method of the rubbery polymer, examples of theinert solvent include saturated hydrocarbons and aromatic hydrocarbons,more specifically, aliphatic hydrocarbons such as butane, pentane,hexane, pentane and heptane, alicyclic hydrocarbons such ascyclopentane, cyclohexane, methylcyclopentane and methylcyclohexane andaromatic hydrocarbons such as benzene, toluene and xylene andhydrocarbons as a mixture thereof.

As a polymerization initiator, an anionic polymerization initiator isemployed. Preferred are organic alkali metal compounds and organicalkaline earth metals, of which the organolithium compounds areparticularly preferred. Examples of the organolithium compounds includethose containing any one of organolithium polymerization initiatorhaving polymerization initiating capacity and having a low molecularweight, organolithium compounds of a solubilized oligomer, those having,in one molecule thereof, one lithium or plural lithiums and thosehaving, in the bonding manner of an organic group and lithium, acarbon-lithium bond, a nitrogen-lithium bond or a tin-lithium bond.Specific examples include monoorganolithium compounds such as n-butyllithium, sec-butyl lithium, t-butyl lithium, n-hexyl lithium, benzyllithium, phenyl lithium and stilbene lithium; polyfunctionalorganolithium compounds such as 1,4-dilithiobutane, reaction product ofsec-butyl lithium and diisopropylbenzene, 1,3,5-trilithiobenzene,reaction product of n-butyl lithium, 1,3-butadiene and divinylbenzene,reaction product of n-butyl lithium and polyacetylene compound, andcompounds having a nitrogen-lithium bond such as dimethylaminolithium,dihexylaminolithium and hexamethyleneiminolithium, of which the n-butyllithium and se-butyl lithium are particularly preferred. Theseorganolithium compounds may be used either singly or in combination. Inthe polymerization reaction, it is possible to add an aprotic polarcompound, for example, an ether such as diethyl ether, diethylene glycoldimethyl ether, tetrahydrofuran or 2,2-bis(2-oxolanyl)propane, or anamine such as triethylamine or tetramethylethylene diamine in order torandomly copolymerize styrene with a conjugated diene.

The polymerization reaction is conducted under the ordinarily employedconditions, for example, at a polymerization temperature of 20 to 150°C. and at a final polymer concentration ranging from 5 to 30 wt. %. Thepolymerization temperature is controlled by the feed temperature of amonomer or solvent, concentration of the monomer or cooling or heatingfrom the outside of a reactor.

The rubbery polymer to be used in the invention must contain, in anamount exceeding 60 wt. %, a modified component available by reacting adiene polymer having an active end with a polyfunctional compoundhaving, in the molecule thereof, at least 2 epoxy groups.

To industrially produce such a rubbery polymer having a highmodification ratio, it is necessary to efficiently prepare, prior to themodification reaction, a diene polymer having an active end by the wellcontrolled method. An industrially available monomer or solvent usuallycontains various harmful impurities. When they react with the active endof the polymer during polymerization, thereby causing a terminatingreaction or transferring reaction, the active end of the polymerdecreases, which makes it difficult to produce the polymer of thepresent invention containing a modified component in an amount exceeding60 wt. %. Particularly upon polymerization at a temperature as high as80° C. or greater, influence of impurities such as alkene, acetylene orwater cannot be neglected. It is necessary to feed a polymerizationreactor with a monomer and a solvent each containing less impurities andto control the polymerization temperature in order to produce a dienepolymer having the structure as specified by the invention.

In the invention, the amount of all the impurities in the monomer andsolvent to be fed to the polymerization reactor must be reduced to lessthan 0.40 equivalent, preferably 0.30 equivalent or less based on aninitiator to be fed to the polymerization reactor. Specific examples ofthe impurities in the conjugated diene monomer include compoundsreactive with plural moles of an organic alkali metal such as vinylacetylene, 1,2-butadiene or butin-1, and compounds reactive with anequimolar amount of an organic alkali metal such as aldehyde; those ofthe impurities in the styrene monomer include compounds reactive with anequimolar amount of an organic alkali metal such as phenylacetylene andbenzaldehyde; and those of the impurities common to various monomers andsolvents include compounds reactive with 2 moles of an organic alkalimetal such as TBC, a short stop and compounds reactive with an equimolaramount of an organic alkali metal such as water. In the invention, it ispreferred to conduct calculation with regards to the compound to bereacted with plural moles of the organic alkali metal, supposing thatthe compound is reacted with two moles of the organic alkali metal.

To lessen the influence of such impurities, use or a raw materialcontaining impurities as less as possible is of course preferred, butpractically, it is the common practice to use a raw material containingimpurities and remove them by the chemical engineering method such asdistillation or adsorption. Such a method is however not sufficientlyeffective and it takes a tremendous cost to obtain sufficient effects.Even a trace amount of impurities adversely affects the presentinvention because the molecular weight is which so that as a method forreducing the influence of impurities more than usual, reaction of them,prior to feeding the polymerization reactor with a monomer and asolvent, with an organic metal compound in an amount corresponding toimpurities, more specifically, with a polymerization catalyst, therebysubstantially inactivating the impurities is preferred. Single use orcombination of the above-described methods makes it possible to largelylower deactivation of the active end due to the impurities contained inthe monomer solution to be fed to the polymerization reactor, therebyconducting modification reaction at an industrially advantageousefficiency at a temperature exceeding 80° C., preferably 120° C. orless.

As the modifier to be used for obtaining the polymer of the inventioncontaining the modified component, a polyfunctional compound having, inthe molecule thereof, at least two epoxy groups is employed. Anypolyfunctional compound having, in the molecule thereof, at least twoepoxy groups is usable. Specific examples include polyglycidyl ethers ofa polyhydric alcohol such as ethylene glycol diglycidyl ether andglycerin triglycidyl ether, polyglycidyl ethers of an aromatic compoundhaving at least two phenol groups such as diglycidylated bisphenol A,polyepoxy compounds such as 1,4-diglycidylbenzene,1,3,5-triglycidylbenzene and polyetpoxylated liquid polybutadiene,epoxy-containing tertiary amines such as4,4′-diglycidyl-diphenylmethylamine and4,4′-diglycidyl-dibenzylmethylamine, and diglycidylamino compounds suchas diglycidyl aniline, diglycidyl orthotoluidine, tetraglycidylmethaxylenediamine, tetraglycidyl-p-phenylenediamine, diglycidylaminomethylcyclohexane and tetraglycidyl-1,3-bisaminomethylcyclohexane.Preferred are the polyfunctional compounds having, in the moleculethereof, at least two epoxy groups and at least one nitrogen-containinggroup. More preferred are the polyfunctional compounds of the followingformula:

wherein, R¹ and R² each independently represents a C₁₋₁₀ hydrocarbongroup or a C₁₋₁₀ hydrocarbon group having an ether or a tertiary amine,R³ and R⁴ each independently represents hydrogen, a C₁₋₂₀ hydrocarbongroup or a C₁₋₂₀ hydrocarbon group having an ether or tertiary amine, R⁵represents a C₁₋₂₀ hydrocarbon group or a C₁₋₂₀ hydrocarbon group havingat least one group selected from ethers, tertiary amines, epoxy,carbonyl and halogens, and n stands for 1 to 6.

More preferred are the polyfunctional compounds having a diglycidylaminogroup. The number of the epoxy groups in the molecule must be at leasttwo, preferably at least 3 and more preferably at least 4. Neitherpolyfunctional compounds having, in the molecule thereof, a functionalgroup which reacts with the active end of the polymer, therebyinactivating it, for example, an active-hydrogen-containing functionalgroup such as hydroxyl, carboxyl or primary or secondary amino group;nor polyfunctional compounds having, in the molecule thereof, afunctional group which eliminates an alcohol or amine, such as ether oramide are preferred. The polyfunctional compound may contain afunctional group which is reactive with the active end of the polymerand is bonded thereto such as carbonyl or halogen.

The polyfunctional compound having, in the molecule thereof, at leasttwo epoxy groups is preferably reacted with the active end of thepolymer so that an amount of the epoxy group of the polyfunctional groupto be reacted with the active end of the polymer exceeds 0.6 equivalentand a ratio of the molecule of the polyfunctional compound to the activeend of the polymer to be reacted therewith is not greater than 10 timesthe mole. Below the above-described range, the modified component of theinvention does not exceed 60 wt. % in the case of the active end of thepolymer obtained by polymerization in the presence of a monofunctionalinitiator. Above the above-described range, on the other hand, thepolyfunctional compound having an unreacted epoxy group increases,resulting in deterioration in the performance.

By the reaction between the active end of the polymer and epoxy group, ahydroxyl group is introduced into the polymer chain. When the epoxygroup of the polyfunctional group exceeds 0.6 equivalent but not greaterthan 1 equivalent of the active end of the polymer, a large portion ofthe active end of the polymer reacts with the epoxy group of thepolyfunctional compound and causes coupling reaction of pluralmolecules, resulting in the formation of a modified polymer moleculehaving plural hydroxyl groups. When the epoxy group of thepolyfunctional group exceeds 1 equivalent of the active end of thepolymer, formed are both the polymer molecule having plural hydroxylgroups and a modified polymer molecule— which contains both a hydroxylgroup produced by the reaction of the active end of the polymer with theepoxy group and an unreacted epoxy group in the polyfunctional compoundmolecule bonded to the polymer—. By the use of a polyfunctional compoundhaving, in the molecule thereof, at least two epoxy groups and at leastone nitrogen-containing group, a nitrogen-containing group together witha hydroxyl group formed by the reaction of the active end of the polymerwith the epoxy group is introduced.

A specific rubbery polymer to be used in the invention must contain thecomponent, which has been modified by the polyfunctional compound, in anamount exceeding 60 wt. % based on the whole polymer. Preferred is 70wt. % or greater. The greater the content of the modified component, thebetter the effects of silica as a filler. The content of the modifiedcomponent can be measured by chromatography permitting separation of thecomponent into modified one and unmodified one. This chromatography iseffected, for example, by using a GPC column which adopts, as a filler,a polar substance such as silica for adsorbing thereto the modifiedcomponent and determining the amount of the component by using anon-adsorptive component as an internal standard; or by measuring theGPCs of the polymer before and after modification and calculating theamount of the modified portion based on a change in its shape ormolecular weight.

The molecular weight distribution Mw/Mn of the rubbery polymer as thecomponent (A-1) to be used in the present invention ranges from 1.05 to3.0. The molecular weight distribution can be measured using GPC basedon the molecular weight of standard polystyrene. Molecular weightdistribution less than 1.05 deteriorates processability and at the sametime, does not permit easy industrial production. At a molecular weightdistribution exceeding 3.0, on the other hand, the rubber compositionavailable from the resulting rubbery polymer has deteriorated mechanicalstrength.

The polymer having a molecular weight distribution of 2.2 or greater hasadvantages in excellent processability upon kneading, not a large torqueupon processing and short kneading time. When the polymer has amolecular weight distribution less than 2.2, on the other hand,processability is usually inferior. Particularly when silica isincorporated, the torque upon processing becomes large. In such a case,a large amount of carbon black was conventionally used in combination.In the invention, affinity with silica is heightened so that even if theamount of carbon black is small, the processability is excellent; therubber composition thus obtained is well balanced between low rollingresistance and wet skid resistance; and strength properties areimproved.

The rubbery polymer to be used in the invention as the component (A-1)must have a weight-average molecular weight of 100,000 to 2,000,000. Theweight-average molecular weight is measured by GPC based on themolecular weight of standard polystyrene. Weight-average molecularweights less than 100,000 deteriorate the strength and wear resistanceof the resulting rubber composition, while those exceeding 2,000,000lower the processability markedly, making it difficult to obtain arubbery composition.

The Mooney viscosity (MV-M) of the rubbery polymer to be used in theinvention as the component (A-1) preferably ranges from 20 to 200. ThisMooney viscosity is Mooney viscosity ((ML1+4 (100° C.)) as measured at100° C. by using a Mooney viscometer specified as standards. When theMooney viscosity ((ML1+4 (100° C.)) exceeds approximately 150 and cannotbe measured easily at 100° C., the viscosity measured, for example, at130° C. is converted to that at 100° C. Mooney viscosities (MV-M) lessthan 20 lower the strength and wear resistance of the resulting rubbercomposition. Those exceeding 200, on the other hand, cause a markeddeterioration in the processing performance, making it difficult toproduce a rubber composition. Mooney viscosities (MV-M) within 25 to 180are more preferred.

The rubbery polymer to be used as the component (A-1) of the inventioncan be provided for practical use as an oil extended rubber produced,for facilitating its processing, by adding 20 to 60 parts by weight ofthe ordinarily-employed rubber extending oil based on 100 parts byweight of a rubber.

The rubbery polymer to be used as the component (A-1) of the inventionpreferably has a glass transition point ranging from −100 to 0° C. sothat the rubber composition obtained as a final product will exhibitrubber elasticity. That ranging from −95 to −10° C. is more preferred.The range of the glass transition point of the rubbery polymer to beused in the invention is selected depending on the using purpose of therubber composition. For example, when low-temperature performances areimportant, a rubbery polymer having a glass transition point within alow temperature range is subjectively selected. When damping capacity isrequired, a rubbery polymer having a glass transition point within ahigh temperature range is subjectively selected. The glass transitionpoint can be controlled by the composition of a conjugated diene andstyrene constituting the rubbery polymer or by the ratio or themicro-structure (ratio of 1,4-bond to 1,2- and 3,4-bonds) in the polymerchain when the conjugated diene is butadiene or isoprene. When therubbery polymer of the invention is polybutadiene, the 1,2-bond contentof the microstructure of butadiene is preferably 10 to 80%. When therubbery polymer of the invention is a styrene-butadiene randomcopolymer, on the other hand, it is preferred that the styrene contentis 5 to 45% and the 1,2-bond content of the micro-bond of a butadieneportion is 10 to 70%.

As the rubbery polymer to be used as the component (A-1) of theinvention, one or more rubbery polymers may be used. When polybutadieneand a styrene-butadiene copolymer are used in combination, the lattermay be a combination of styrene-butadiene copolymer rubbers different inmolecular weight-molecular weight distribution or a combination of thosedifferent in a glass transition point.

When as a preferred mode of the invention, 10 to 90 parts by weight of astyrene-butadiene copolymer rubber containing a modified component in anamount of 70 wt. % or greater, and having a glass transition pointranging from −80 to −20° C., a molecular weight distribution of 1.05 orgreater but less than 2.2, and a Mooney viscosity (ML1+4 (100° C.)) of20 or greater but less than 100; and 90 to 10 parts by weight of astyrene-butadiene copolymer rubber containing a modified component of 70wt. % or greater, and having a glass transition point ranging from −50to −20° C., a molecular weight distribution ranging from 2.2 to 3.0 anda Mooney viscosity (ML1+4 (100° C.)) ranging from 100 to 200 are used asthe component (A-1) the resulting rubber composition is excellent in anyone of processability, strength properties, and a balance between lowrolling resistance and wet skid resistance.

As the component (B), rubber extending oils which contain only a smallamount of a polynuclear aromatic component such as MES, T-DAE or T-RAEand therefore are not harmful for environment are usable as well as theconventionally used aromatic, naphthene and paraffin ones. In theinvention, the rubber extending oil is used in an amount of 1 to 100parts by weight based on 100 parts by weight of the raw material rubber.The amount of the rubber extending oil varies depending on the amountsof a reinforcing silica filler and reinforcing carbon black which willbe described later and it is used to adjust the elastic modulus of thevulcanized mixture. Amounts of the rubber extending oil exceeding 100parts by weight deteriorate the hysteresis loss performance and wearresistance of the resulting rubber composition and are therefore notpreferred. Amounts of the rubber extending oil ranging from 5 to 60parts by weight are preferred.

With regards to the component (C) of the present invention, any one ofwet-process silica, dry-process silica and synthetic silicate typesilica is usable as the reinforcing silica. Silica having a smallparticle size has high reinforcing effects and grip performanceimproving effects. Small-particle-size and high aggregation type silicais preferred. The reinforcing silica of the present invention is used asa reinforcing-effect-equipped silica in an amount of 25 to 100 parts byweight based on 100 parts by weight of the raw material rubber. Amountsless than 25 parts by weight deteriorate physical performances includingstrength, while those exceeding 100 parts by weight lower the rubberperformances, for example, cause an excessive increase of hardness oreven a deterioration of strength. An amount of the reinforcing silica ascomponent (C) is preferably 30 to 90 parts by weight.

The vulcanizing agent and vulcanizing accelerator as the component (D)of the present invention is used in an amount ranging from 1 to 20 partsby weight based on 100 parts by weight of the rubbery polymer. Thetypical vulcanizing agent is sulfur. Sulfur-containing compounds andperoxides may also be used. As the vulcanizing accelerator, sulfenamide,guanidine or thiuram one may be used in a necessary amount.

To the rubbery polymer composition of the present invention, anorganosilane coupling agent can be added as the component (E). Forheightening the coupling action (mutual bonding action) of thereinforcing silica filler with the raw material rubber, thisorganosilane coupling agent is preferably added in an amount of 0.1 to20 wt. % based on the amount of the reinforcing silica as the component(C). Amounts of the organosilane coupling agent exceeding 20 parts byweight impair reinforcing properties. The amount of the organosilanecoupling agent preferably ranges from 0.1 wt. % or greater to less than6 wt. % based on the amount of the reinforcing silica filler.

The organosilane coupling agent has a double bond of the polymer in itsmolecule and groups having affinity or coupling tendency on the surfaceof silica. Examples includebis-[3-(triethoxysilyl)-propyl]-tetrasulfide,bis-[3-(triethoxysilyl)-propyl]-disulfide,bis-[2-(triethoxysilyl)-ethyl]-tetrasulfide,3-mercaptopropyl-trimethoxysilane,3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide and3-triethoxysilylpropylbenzothiazole tetrasulfide. In this invention, therubbery polymer having a specific modified component has a high bondingperformance with the reinforcing silica so that a high-performancerubber composition is available even by not using an organosilanecoupling agent or using it in a smaller amount compared with the casewherein another polymer is used.

In the rubber composition of the invention, reinforcing carbon black canbe used as the component (F) in an amount with an extent not impairingthe performance of the reinforcing silica. Any one of carbon blacks suchas FT, SRF, FEF, HAF, ISAF and SAF is usable as the reinforcing carbonblack. Carbon black having a nitrogen adsorption specific surface areaof 50 mg/g or greater and an DBP oil absorption amount of 80 ml/100 g ispreferred. The reinforcing carbon black is added in an amount of 0.1 to100 parts by weight based on 100 parts by weight of the raw materialrubber and total amount of the reinforcing silica (component (C)) andcarbon black (component (F)) is preferably 30 to 150 parts by weight.Outside the above-described range, performances of a rubber satisfyingthe object of the present invention are not attained. The amount ofcarbon black (component (F)) ranging from 0.1 part by weight or greaterto less than 25 parts by weight is more preferred. Amounts within such arange further improve the balance of the resulting rubber compositionbetween low rolling resistance and wet skid resistance.

As the raw material rubber in the present invention, only the component(A-1) can be used, or alternatively, that comprising 15 to 99 wt. % offthe component (A-1) and, as a component (A-2), 1 to 85 wt. % of avulcanizable rubber polymer other than the component (A-1) can be used.Since the rubbery polymer as the component (A-1) has large performanceimproving effects, addition of it makes it possible to produce, even ina small content in the raw material rubber, a vulcanized rubbercomposition having an improved performance. As the component (A-2), atleast one selected from synthetic rubbers and natural rubbers is used asneeded. Specific examples of the component (A-2) include butadienerubber, styrene-butadiene rubber, styrene-isoprene-butadiene rubber andsynthetic polyisoprene rubber, which are other than the component (A-1),and butyl rubber and natural rubbers. At least one selected from them isused. Examples of the butadiene rubber as component (A-2), other thanthe component (A-1), include high-cis butadiene rubber available usingany one of cobalt, nickel, neodymium and uranium catalysts, low-cisbutadiene rubber available using a lithium catalyst and mediumhigh-vinyl butadiene rubber; those of the styrene-butadiene rubber otherthan the component (A-1) include emulsion-polymerized styrene-butadienerubber having a styrene content of 3 to 50 wt. % andsolution-polymerized styrene-butadiene rubber having a styrene contentof 3 to 50 wt. % and a 1,2-bond content, at the butadiene moiety, of 10to 80%; those of the styrene-isoprene-butadiene rubber other than thecomponent (A-1) include styrene-isoprene-butadiene rubber having astyrene content of 3 to 40 wt. % and an isoprene content of 3 to 40 wt.%; and those of the synthetic polyisoprene rubber other than thecomponent (A-1) include synthetic polyisoprene rubber having acis-1,4-bond content of 90% or greater. After optimization of thephysical properties and processability of this component according tothe using purpose of the rubber composition, it is added. Particularlypreferred as the component (A-2) is the solution-polymerizedstyrene-butadiene rubber, which brings about excellent balance betweenlow rolling resistance and wet skid resistance, thereby satisfying theobject of the invention.

In a preferred mode of the invention, use of, as the component (A-1), aspecific polymer containing a modified component in an amount of 70 wt.% or greater and having a glass transition point ranging from −80 to−20° C., and, as the component (A-2), a solution-polymerizedstyrene-butadiene copolymer rubber having a glass transition pointranging from −50 to −20° C. and a Mooney viscosity (ML1+4 (100° C.)) of100 or greater is desired.

Another preferred example of a solution-polymerized styrene-butadienecopolymer rubber is that having a Mooney viscosity (ML1+4 (100° C.))ranging from 150 or greater and a molecular weight distribution (Mw/Mn)ranging from 1.4 to 2.2. By using it in combination with the specificrubbery polymer as the component (A-1) of the present invention, arubber composition having good strength properties and an excellentbalance between low rolling resistance and wet skid resistance can beproduced.

As the component (A-2), an emulsion-polymerized styrene-butadienecopolymer rubber having a styrene content of 30 to 50 wt. % and a Mooneyviscosity (ML1+4 (100° C.)) ranging from 100 or greater is also usable.

In the present invention, another additive such as zinc white, stearicacid, vulcanizing assistant, antioxidant and/or processing aid is addedas needed in an amount satisfying the object of the present invention,for example, 0.1 to 20 parts by weight.

In the present invention, a diene polymer rubber vulcanizate is providedby kneading, at least once, the component (A-1), or the components(A-1), (A-2), (B) and (C), and optionally the component (E), thecomponent (F) and another additive in a known enclosed mixer such asinternal mixer under the conditions permitting the kneading anddischarging temperature of 135 to 180° C., thereby controlling the boundrubber content after mixing (a ratio of the raw material rubbercomponent bonded to the reinforcing filler) to 30 to 70 wt. %; adding avulcanizing agent and a vulcanizing accelerator as the component (D);and kneading them in a known mixer such as internal mixer or mixing rollto control the kneading and discharging temperature to 120° C. or less,thereby vulcanizing. At the kneading and discharging temperature outsidethe above-described range, a diene polymer rubber vulcanizate excellentin the balance between low rolling resistance and wet skid resistanceand having improved strength properties is not available and thereforethe object of the invention cannot be satisfied. The bound rubbercontent is required to be 30 to 70 wt. %. At a bound rubber content lessthan 30 wt. %, a diene polymer rubber vulcanizate excellent in thebalance between low rolling resistance and wet skid resistance andhaving improved strength properties is not available and therefore, theobject of the present invention cannot be satisfied. Bound rubbercontents exceeding 70 wt. %, on the other hand, increase the torque uponkneading, thereby making it difficult to conduct processing. The boundrubber content ranging from 40 to 70 wt. % is preferred.

In the present invention, it is more preferred to carry outvulcanization by adding an organosilane coupling agent, as the component(E), in an amount of 0.1 wt. % or greater but less than 6 wt. % based onthe amount of the reinforcing silica, kneading the mixture at least onceunder the conditions permitting the kneading and discharging temperatureof 135 to 180° C., thereby controlling the bound rubber content aftermixing (a ratio of the raw material rubber component bonded to thereinforcing filler) to 30 to 70 wt. %, adding a vulcanizing agent andvulcanizing accelerator as the component (D), and kneading the mixtureto give the kneading and discharging temperature of 120° C. or less.

Moreover, it is preferred to conduct vulcanization by kneading,depending on the heating loss (Mo) of the reinforcing silica as thecomponent (C), the components at least once under the conditionspermitting the following kneading and discharging temperature (Td):

135≦Td≦180° C. when 1%≦Mo≦4%

(15×Mo+75)° C.<Td≦180° C. when 4%<Mo≦6%, and

165° C.<Td≦180° C. when 6%<Mo≦10%, thereby controlling the bound rubbercontent after kneading (a ratio of the raw material rubber componentbonded to the reinforcing filler) to 30 to 70 wt. %, adding avulcanizing agent and a vulcanizing accelerator as the component (D),and kneading the mixture to give the kneading and dischargingtemperature of 120° C. or less. The diene polymer rubber vulcanizateavailable in this manner is excellent in the balance of low rollingresistance and wet skid resistance and improved in strength properties.

The performance of the vulcanized rubber composition available as afinal product differs depending on the water content (measured as aheating loss (Mo) at 105° C. after 8 hours) of the reinforcing silicadue to the difference in its production process. In the presentinvention, it is preferred to adjust the kneading temperature of thecomponents, depending on the heating loss of the reinforcing silica.Silicas different in heating loss are available by dryingcommercially-available silica, whose heating loss is approximately 6 to8%, at a temperature range of 100 to 120° C. under normal pressure. Forexample, silica having a heating loss of 1 to 4 wt. % can be obtained bydrying commercially-available silica at 105° C. under normal pressurefor approximately 1 to 8 hours.

The optimum temperature varies depending on the heating loss of silica,because heating loss of reinforcing silica, that is, water adsorbed tothe reinforcing silica becomes an inhibitory factor against the reactionbetween the reinforcing silica and modified polymer. When silica havinga higher heating loss is used, rubber is not bonded to silicasufficiently at the kneading and discharging temperature lower than thelower limit of the range, while scorch of the composition andcrosslinking reaction happen at the kneading and discharging temperaturehigher than the upper limit of the range. The temperature outside therange is therefore not preferred. Such adjustment of the kneading anddischarging temperature makes it possible to bring about effects forimproving the productivity on the industrial scale.

In the present invention, a diene polymer rubber vulcanizate availableby vulcanizing in a conventional manner, for example, at 120 to 200° C.,preferably 140 to 180° C. exhibits its performance as it is.

The rubbery polymer according to the invention is suitably used, in theform of a diene polymer rubber vulcanizate, for tire tread mixturestypified by high-performance tires and all-season tires, but it is alsoapplied to another tire, rubber vibration isolator, belt, industrialgood, footwear and the like.

The present invention will hereinafter be described in detail byexamples and comparative examples. It should however be borne in mindthat the present invention is not limited to or by them.

REFERENCE EXAMPLE 1 Manufacturing Process of SBR—1

A thermostatic autoclave having an internal volume of 10 liter andequipped with a stirrer and a jacket was used as a reactor. In thereactor, 645 g of impurity-removed butadiene, 280 g of styrene, 5500 gof cyclohexane and 0.70 g of 2,2-bis(2-oxolanyl)propane as a polarsubstance were charged and the internal temperature of the reactor wasadjusted to 30° C. A cyclohexane solution containing 0.85 g of n-butyllithium was fed as a polymerization initiator to the reactor. Afterinitiation of the reaction, the internal temperature of the reactorgradually increased by the heat generated upon polymerization. For 5minutes from 7 minutes to 12 minutes after the addition of thepolymerization initiator, 75 g of butadiene was fed at a rate of 15g/min. The final internal temperature in the reactor reached 75° C.After completion of the polymerization reaction, a portion of thepolymer solution was sampled. The Mooney viscosity of the pre-modifiedpolymer as measured after the removal of the solvent at 100° C. was 7.As a modifier, 1.2 g of tetraglycidyl-1,3-bisaminomethylcyclohexane wasadded to the reactor and modification reaction was conducted whilemaintaining the temperature at 75° C. for 5 minutes. After addition ofan antioxidant to this polymer solution, the solvent was removed,whereby a styrene-butadiene copolymer (Sample A) having a modifiedcomponent was obtained. The modified polymer had a Mooney viscosity of65 as measured at 100° C.

Analysis of the sample A resulted in 28% of a bond styrene content and72% of a bonded butadiene content. It was also found that the 1,2-bondcontent of the microstructure of the butadiene moiety as measured inaccordance with Hampton's method from the measuring results using aninfrared spectrophotometer was 52%, and the weight-average molecularweight (Mw), number-average molecular weight (Mn) and molecular weightdistribution (Mw/Mn) were 563000, 423000 and 1.33, respectively in termsof polystyrene as measured by GPC; and a modifying ratio as determinedfrom GPC using a silica adsorption column was 83%.

In addition, styrene-butadiene copolymer rubbers were prepared asSamples B to P and Samples BA to BE in a similar manner to Sample Aexcept for a change of the bonded styrene content, 1,2-bond content of abutadiene moiety, Mooney viscosity, glass transition point, molecularweight distribution, modification ratio or modifying agent.

The samples O and P having a high molecular weight were prepared as aproduct extended with 37.5 parts by weight of an aromatic oil. Amongthose samples, Samples A, B, C, H, J, K, L, N, N, O, BA, BB, BC and BDare polymers specified as the component (A-1) of the composition of theinvention, while Samples D, E, F, G, P and BE are prepared forcomparison and are polymers outside the range specified as the component(A-1) of the composition of the invention.

REFERENTIAL EXAMPLE 2 Manufacturing Process of SBR—2

Two autoclaves each having an internal volume of 10 liters, having aninlet at the bottom and an outlet at the top and being equipped with astirrer and a jacket were connected in series as reactors. After mixing16.38 g/min of butadiene, 8.82 g/min of styrene and 132.3 g/min ofn-hexane, the resulting mixture solution was allowed to pass through adehydration column filled with active alumina. Impurities were removedby mixing n-butyl lithium at a rate of 0.0046 g/min in a static mixer.The residue was then continuous fed from the bottom of the first reactorthrough a constant delivery pump. The reactor was fed directly with2,2-bis(2-oxolanyl)propane at a rate of 0.028 g/min as a polar substanceand n-butyl lithium at a rate of 0.070 g/min as a polymerizationinitiator. The internal temperature of the reactor was maintained at 86°C. From the top portion of the reactor, the polymer solution wascontinuously taken out and fed to the second reactor. It was found thatafter the first reactor became stable, the resulting pre-modifiedpolymer had a Mooney viscosity of 55 as measured at 100° C. At thetemperature of the second reactor maintained at 80° C., 0.009 g/min(equivalent ratio relative to active lithium=0.9) oftetraglycidyl-1,3-bisaminomethylcyclohexane was added from the bottom ofthe reactor to effect modification reaction. An antioxidant wascontinuously added to this polymer solution and modification reactionwas terminated. By the removal of the solvent, the targetstyrene-butadiene copolymer having a modified component was obtained. Itwas found that this modified polymer had a Mooney viscosity of 163 asmeasured at 100° C. To 100 parts by weight of this polymer solution,37.5 parts by weight of an aromatic oil (“X-140”, trade name; product ofJapan Energy Co., Ltd.) was added to yield an oil-extended oil (SampleQ).

As a result of analysis of the sample Q, the bonded styrene content was35%; the bonded butadiene content was 65%; the 1,2-bond content of thebutadiene moiety as determined in accordance with the Hampton's methodby calculating the results measured by an infrared spectrophotometer was35 mole %; the Mooney viscosity (ML1+4, 100° C.) after oil extension was65; and the glass transition point was −34° C. According to themolecular weight distribution by GPC (detector: RI) with THF as asolvent, the weight-average molecular weight (Mw), the number-averagemolecular weight (Mn), and the molecular weight distribution (Mw/Mn)were 656000, 264000 and 24800, respectively, each in terms ofpolystyrene; and the GPC curve had a monomodal shape. The modificationratio as determined from GPC curve using a silica series adsorptioncolumn was found to be 65%.

In a similar manner to the continuous polymerization method employed forpreparing Sample Q except for a change of the amount of BuLi, the amountof the modifying agent and the kind of the modifying agent, Samples R toAC different in structure were obtained.

A commercially-available styrene-butadiene rubber, butadiene rubber andnatural rubber as shown in Table 4 were also employed as samples.

The analysis values of these samples are shown in Tables 1 to 4. Thesesamples were analyzed in accordance with the method as described below.

1) Bonded Styrene Content

The sample was dissolved in chloroform and the bonded styrene content (S(wt. %)) was measured from the absorption of styrene by a phenyl groupat 254 nm.

2) The Microstructure of a Butadiene Moiety

The sample was dissolved in carbon disulfide and the microstructure ofthe butadiene moiety was determined by measuring the infrared rayspectrum within a range of 600 to 1000 cm-1 by using a solution cell,and calculating from a predetermined absorbance in accordance with theequation of the Hampton's method.

3) Glass Transition Temperature

It was measured at a heating rate of 10° C./min by using DSC. The on setpoint was designated as Tg.

4) Mooney Viscosity

The viscosity four minutes after preheating at 100° C. for 1 minute wasmeasured in accordance with JIS K 6300.

5) Molecular Weight and Molecular Weight Distribution

The chromatogram was measured by GPC having three connected columnsusing a polystyrene gel as a filler. The molecular weight and molecularweight distribution were calculated from the calibration curve based onstandard polystyrene.

6) Modification Ratio

By making use of the properties of the modified component to adsorb to aGPC column using silica gel as a filler, both chromatogram's of GPC ofpolystyrene gel (“Shodex” of Showa Denko K.K.) and GPC of silica column(“Zorbax” of Dupont) were measured with regards to the test solutioncontaining a sample and a low-molecular-weight internal standardpolystyrene. The adsorption amount to the silica column was measuredfrom their difference and modification ratio was determined.

EXAMPLES

Rubber mixtures were obtained using Samples shown in Tables 1 to 4 asraw material rubbers and kneading the blending formulations as shown inTable 5 by the below-described mixing method.

Kneading Method

In an enclosed kneader (internal volume: 1.7 liter) equipped with athermostat using water circulated from the outside, a raw materialrubber, filler (silica and carbon black), organosilane coupling agent,aromatic oil, zinc white and stearic acid were kneaded (the kneadingprocedure will be shown in Table 6) as the first-stage kneading underthe conditions of a filling rate of 65% and rotational number of therotor of 66/77 rpm. Upon kneading, the temperature of the enclosed mixerwas adjusted and rubber compositions different in discharge temperaturewere obtained.

After cooling of the mixture thus obtained to room temperature, anantioxidant was added thereto and then, kneading was conducted again asthe second-stage kneading to improve dispersion of silica. In this case,the discharge temperature was adjusted by the temperature of the mixer.

After cooling, sulfur and a vulcanizing accelerator were kneaded as thethird-stage kneading in an open roll set at 70° C.

The resulting kneaded mass was molded and vulcanized under a vulcanizingpress at 160° C. for a predetermined time. The below-described physicalproperties were measured as the performances of a tire.

1) Bound Rubber Content

The composition (0.2 g) sampled after completion of the second-stagekneading was cut into square pieces of about 1 mm and placed in aHarris's basket (made of a 100-mesh metal mesh). These pieces wereweighed. After immersion in toluene for 24 hours, they were weighedagain. From the amount of the component not dissolved in toluene, theamount of the rubber bound to the filler was calculated and designatedas the bound rubber content.

2) Mooney Viscosity of the Mixture

Viscosity four minutes after preheating for 1 minute at 130° C. and 2revolutions was measured in accordance with JIS K 6300 by a Mooneyviscometer. The mixture having a Mooney viscosity largely exceeding 80is inferior in processability. When the Mooney viscosity is not greaterthan 30, large adhesion prevents smooth processing.

3) 300% Modulus and Tensile Strength

Measured in accordance with the tensile test method of JIS K 6251.

4) Fuel-cost Saving Performance

Tested in Tan δ at 50° C. Measured by ARES viscoelasticity tester ofRheometric Scientific at a Frequency of 10 Hz, distortion of 3% and 50°C. in accordance with a torsion system. The smaller the numeral, thebetter the fuel-cost-saving performance.

5) Wet Skid Resistance

Tested in Tan δ at 50° C. Measured by ARES viscoelasticity tester ofRheometric Scientific at a frequency of 10 Hz, distortion of 3% and 50°C. in accordance with a torsion system. The greater the numeral, thebetter the wet skid resistance.

Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-4

Vulcanized rubber compositions were prepare using, as a raw materialrubber, Samples A, B and C having a modified component as specified bythe invention, Sample D which has the modified component as specified bythe invention but in an amount outside the range of the invention,Samples E and F having a modified component other than that specified bythe invention, and unmodified Sample G, each in accordance with thesilica-containing formulation (Formulation S-1) as specified by theinvention. Their performances were evaluated. As the silica, that havinga water adsorption amount Mo (heating loss content: drying under normalpressure at 105° C. for 8 hours) of 5.4% was employed. The measurementresults are shown in Table 7.

As is apparent from Table 7, the vulcanized rubber compositions ofExamples 1-1 to 1-3 using the rubbery polymer within the range asspecified by the invention are superior in fuel-cost-saving performanceand wet skid resistance to the compositions of Comparative Examples 1-1to 1-4 in the same silica-containing formulation.

Examples 2-1 and Comparative Examples 2-1 to 2-4

Vulcanized rubber compositions were prepared, in different formulationsas shown in Table 8, by using Sample A which was a specificstyrene-butadiene rubber of the invention, Sample D for which amodifying agent as specified by the invention was used at a modifyingamount outside the range of the invention, Sample RB which was acommercially-available emulsion-polymerized SBR and Sample RC which wasa commercially-available solution-polymerized SBR. The performances ofthem were measured and their results are shown in Table 8. As thesilica, that having a water adsorption amount Mo of 5.4% was used.

As is apparent from the results of Table 8, the silica-containingcomposition according to the invention exhibited good fuel-cost-savingperformance compared with the composition of Comparative Example 2-1 inwhich carbon black was incorporated (Composition S-11). The compositionof Example 2-1 was markedly superior in fuel-cost-saving performance tothe carbon-black-containing composition of Comparative Example 2-3 usingemulsion polymerized SBR (RB); and was improved much in wet skidresistance and also in fuel-cost-saving performance compared with thecarbon-black-containing composition of Comparative Example 2-4 usingSample RC, that is, the commercially-available solution-polymerized SBR.

Examples 3-1 to 3-4

Vulcanized rubber compositions were prepared in a similar manner toExample 1 by using Samples H, J and K which had a styrene-butadienerubber structure within the range specified by the invention. As thesilica, that having a water adsorption amount Mo of 5.4% was employed.The evaluation results of the performances of these compositions areshown in Table 9.

As is apparent from the results of Table 9, the vulcanized rubbercompositions of Examples 3-1 to 3-4 using the samples within the rangeof the invention showed good processability, tensile strength, andbalance between fuel-cost-saving performance and wet skid resistance.

Examples 4-1 to 4-2 and Comparative Examples 4-1,to 4-2

Vulcanized rubber compositions rich in a filler were obtained in asimilar manner to Example 1 by using Samples O and Q which had astyrene-butadiene rubber structure within the range specified by theinvention. As the silica, that having a water adsorption amount Mo of5.4% was employed. For comparison, a vulcanized rubber composition wasprepared using solution-polymerized styrene-butadiene Sample P which wasoutside the range of the invention. Evaluation results of theperformances of these compositions are shown in Table 10.

As is apparent for the results of Table 10, the vulcanized rubbercomposition of Examples 4-1 and 4-2 using the samples which were withinthe range of the invention exhibit good processability and good balancebetween fuel-cost-saving performance and wet skid resistance. Thecomposition using Sample P which was outside the range of the inventionhas a high viscosity and is therefore inferior in processability.

Examples 5-1 to 5-3 and Comparative Examples 5-1 to 5-2

Vulcanized rubber compositions were prepared in accordance with Blendingformulation S-2 as shown in Table 5 by using Sample A which was aspecific styrene-butadiene rubber of the invention and Sample RF whichwas a commercially-available styrene-butadiene rubber obtained bysolution polymerization. As the silica, that having a water adsorptionamount Mo of 5.4% was employed. Evaluation results of their performancesare shown in Table 11.

As is shown in Table 11, the samples within the range of the intentionexhibit good fuel-cost-saving performance, but those outside the rangeof the invention bring about small effects.

Examples 6-1 to 6-16 and Comparative Examples 6-1 to 6-6

Vulcanized rubber compositions as shown in Table 12 were prepared usingSamples A, H, O and L which were styrene-butadiene rubbers within therange of the present invention, a butadiene rubber (Sample RD),emulsion-polymerized styrene-butadiene rubbers (Samples RA and RB) andSamples D, P, R and S which were solution-polymerized SBRs outside therange specified as Component (A-1) of the present invention. As thesilica, that having a water adsorption amount Mo of 5.4% was employed.Evaluation results of their performances are shown in Table 12.

Even if rubber compositions obtained using the sample within the rangeof the invention are blended with a styrene-butadiene rubber orbutadiene rubber, the mixtures exhibit good fuel-cost saving performanceand wet skid resistance while maintaining processability, compared withthe vulcanized rubber compositions of Comparative Examples which areoutside the range of the invention.

Examples 7-1 to 7-2 and Comparative Example 7-1

In Examples 7-1 and 7-2, blend compositions as shown in Table 13 wereprepared by using Samples N and M, that is, styrene-butadiene rubberswithin the range specified by the invention and a natural rubber. Theirperformances were compared pith the composition of Comparative Example7-1 composed solely of a natural rubber. As the silica, that having awater adsorption amount Mo of 5.4% was employed.

As shown in Table 13, the fuel-cost saving performance of the naturalrubber was improved by the addition of the polymer of the presentinvention.

Examples 8-1 and Comparative Examples 8-1 to 8-4

In accordance with the silica-containing formulation (Formulation S-2)as specified by the invention or ordinarily-employed carbon-blackformulation (Formulation R-12), vulcanized rubber compositions wereprepared using, as the raw material rubber, Sample Q having a modifiedcomponent as specified by the invention, Sample T using a modifyingagent outside the range of the invention, Sample X using a modifyingagent as specified by the invention but having a modified componentoutside the range of the invention, and Sample RH which was a standardemulsion-polymerized styrene-butadiene rubber; and their performanceswere evaluated. As the silica, that having a water adsorption amount Moof 5.4% was employed. Results are shown in Table 14.

As is apparent from Table 14, the composition or Example 8-1 is superiorin fuel-cost-saving performance and wet skid resistance to ComparativeExample 8-2 (Sample T) and Comparative Example 8-3 (Sample X), each inaccordance with the silica-containing formulation. It is markedlysuperior in fuel-cost-saving performance to the carbon-black formulation(Comparative Example 8-1) and also exhibits excellent fuel-cost-savingperformance and wet skid resistance compared with the vulcanized rubbercomposition of Comparative Example 8-4 using emulsion-polymerized SBR.

Examples 9-1 to 9-3 and Comparative Examples 9-1 to 9-2

Vulcanized rubber compositions were prepared using Sample A, thestyrene-butadiene rubber as specified in the invention, in accordancewith the blending formulations different in the silica amount or carbonblack amount as shown in Table 5. Measurement results of theirperformances are shown in Table 15. As the silica, that having a wateradsorption amount Mo of 5.4% was employed.

As is apparent from the results of Table 15, the composition usingSample A while keeping the content of silica within the range of theinvention exhibits excellent fuel-cost-saving performance compared withthe comparative composition rich in carbon black.

Examples 10-1 to 10-2 and Comparative Examples 10-1

Vulcanized rubber compositions were prepared using Samples U, V and Zwhich had a styrene-butadiene rubber structure within the range of theinvention in accordance with Blending Formulation S-2 as shown in Table5. For comparison, a vulcanized rubber composition was prepared usingSample W which was a styrene-butadiene rubber outside the range of theinvention. As the silica, that having a water adsorption amount of 5.4%was employed. Evaluation results of their performances are shown inTable 16.

As is apparent from the results of Table 16, the vulcanized rubbercompositions using the samples within the range of the invention exhibitsuperior tensile strength, fuel-cost-saving performance and wet skidresistance, while the vulcanized rubber composition outside the range ofthe invention is inferior in fuel-cost-saving performance.

Examples 11-1 to 11-5 and Comparative Example 11-1

Vulcanized rubber compositions as shown in Table 17 were prepared usingSamples U and V which were styrene-butadiene rubbers within the range ofthe invention, a butadiene rubber (Sample RD), an emulsion-polymerizedstyrene-butadiene rubber (Sample RA) and natural rubber (Sample RE). Asthe silica, that having a water adsorption amount of 5.4% was employed.Evaluation results of their performances are shown in Table 17.

The composition using Sample U or Sample V which was within the range ofthe invention exhibited superior balance between fuel-cost-savingperformance and wet skid resistance to the emulsion-polymerizedstyrene-butadiene rubber composition (Comparative Example 11-1) even ifused as a mixture with a styrene-butadiene rubber.

Examples 12-1 to 12-6 and Comparative Examples 12-1 to 12-3

Vulcanized rubber compositions as shown in Table 18 were prepared usingSample Q which was a styrene-butadiene rubber within the range specifiedby the invention, commercially available emulsion-polymerizedstyrene-butadiene rubbers (Samples RA and RH), and commerciallyavailable solution polymerized styrene-butadiene rubbers (Samples RC, RFand RG). As the silica, that having a water adsorption amount of 5.4%was employed. Evaluation results of their performances are shown inTable 18. Even if blended with such a rubber, the compositions (Examples12-1 to 12-6) using Sample Q which was within the range of the inventionexhibit superior fuel-cost-saving performance and wet skid resistance tothe compositions (Comparative Examples 12-1 to 12-3) outside the rangeof the invention.

Examples 13-1 to 13-8

Compositions of Examples 13-1 to 13-8 which were within the rangespecified by the invention were prepared using Sample J which was withinthe range of the present invention as the raw material rubber, usingsilicas different in heating loss as shown in Table 19, preparingsilica-containing compositions by adjusting the first-stage dischargingtemperature and the second-stage discharging temperature as shown inTable 19, adding a vulcanizing agent and the like at the third-stagetemperature of 70° C., forming the mixture into a predetermined sampleshape and press vulcanizing it at 160° C. for 30 minutes. The evaluationresults of their performances are shown in Table 19.

As is apparent from Table 19, the vulcanized rubber compositions ofExamples 13-1 to 13-7 prepared under conditions within the range of thepresent invention each has a large bound rubber content and exhibitsgood fuel-cost-saving performance while maintaining high wet skidresistance.

Examples 14-1 to 14-6 and Comparative Examples 14-1 to 14-3

Compositions of Examples 14-1 to 14-5 within the range specified by theinvention and Compositions of Comparative Examples 14-1 to 14-3 outsidethe range of the invention were prepared using, as a raw materialrubber, Samples J and Q which were within the range of the invention,changing the amount of an organosilane coupling agent as shown in Tables5 and 20, preparing silica-containing compositions by adjusting thefirst-stage discharging temperature and second-stage dischargingtemperature as shown in Table 20, adding a vulcanizing agent and thelike at the third-stage temperature of 70° C., molding the resultingmixture into a predetermined sample shape and press vulcanizing it at160° C. for 30 minutes. As the silica, that having a water adsorptionamount Mo of 5.4% was employed. Evaluation results of their performancesare shown in Table 20.

As is apparent from Table 20, vulcanized rubber compositions obtained inExamples 14-1 to 14-6 by using the raw material rubber as specified bythe invention and adding an organosilane coupling agent in an amount asspecified by the invention have a high bound rubber content, and exhibitgood polymer/silica dispersion, good processability and goodfuel-cost-saving performance while maintaining high wet skid resistance.The compositions obtained in Comparative Examples 14-1 to 14-3 by usingSample F which was outside the range of the invention each has a smallbound rubber content, and even a vulcanized composition is inferior inreinforcing effects because its 300% modulus is low, and is moreover,inferior in both the fuel-cost-saving performance and wet skidresistance.

Examples 15-1 to 15-6 and Comparative Examples 15-1 to 15-2

Compositions of Examples 15-1 to 15-6 within the range of the presentinvention and those of Comparative Examples 15-1 to 15-2 outside therange of the present invention were prepared by using, as a raw materialrubber, Samples BA, BB and BC which had been modified bytetraglycidyl-1,3-bisaminomethylcyclohexane added in an amount exceeding1 equivalent per active lithium, Sample BD modified by a modifier usedin an amount not greater than 1 equivalent per active lithium, andSample BE for which silicon tetrachloride had been used as a couplingagent according to the blending formulation as shown in Table 5,adjusting the first-stage discharging temperature and second-stagedischarging temperature as shown in Table 21, thereby preparing asilica-containing composition, adding a vulcanizing agent and the likeat the third-stage temperature of 70° C., molding or forming theresulting mixture into a predetermined shape and press vulcanizing it at160° C. for 30 minutes. As the silica, that having a water adsorptionamount Me of 6.5% was employed. Evaluation results of their performancesare shown in Table 21.

As is apparent from Table 21, vulcanized rubber compositions prepared inExamples 15-1 to 15-6 by adding a modifying agent in an amount within aspecified range of the invention exhibit good fuel-cost-savingperformance while showing high wet skid resistance. The compositionsobtained in Comparative Examples 15-1 to 15-2 by using the samplesoutside the range of the present invention but according to the sameblending formulation are, on the other hand, inferior in both fuel-costsaving performance and wet skid resistance.

Examples 16-1 to 16-6 and Comparative Examples 16-1 to 16-3

Rubber compositions were prepared by using, as a raw material rubber,Samples AA to AC and BA, which had been extended by an aromatic oil andto which tetraglycidyl-1,3-bisaminomethylcyclohexane had been added as amodifier in an amount exceeding 1 equivalent per active lithium andSamples T and Y to be used for comparison, adjusting the first-stagedischarging temperature and second-stage-discharging temperature asshown in Table 22, thereby preparing silica-containing compositions,adding a vulcanizing agent and the like at the third-stage temperatureof 70° C., molding or forming the mixtures into a predetermined shapeand then press vulcanizing them at 160° C. for 30 minutes. As thesilica, that having a water adsorption amount Mo of 6.5% was employed.Measurement results of their performances are shown in Table 22.

As is apparent from results of Table 22, the compositions of Examples16-1 to 16-1 prepared using Samples AB, AB, AC and BA to which amodifying agent had been added in an amount within the range of theinvention exhibits good fuel-cost-saving performance, while maintaininghigh skid resistance. The composition using Sample T to which amodifying agent outside the range of the invention had been added andthat using unmodified Sample Y are, on the other hand, inferior infuel-cost-saving performance.

Examples 17-1 to 17-5

Rubber compositions were obtained by using, as a raw material rubber,Samples A, AA, BA and Q shown in Table 23, each within the range of thepresent invention, adjusting the first-stage discharging temperature andsecond-stage discharging temperature as shown in Table 23, therebypreparing silica-containing compositions, adding a vulcanizing agent andthe like at the third-stage temperature of 80° C., molding or formingthe mixtures into a predetermined shape and press vulcanizing them at160° C. for 30 minutes. As the silica, that having a water adsorptionamount Mo of 5.4% was employed. Measurement results of theirperformances are shown in Table 23.

As is apparent from the results of Table 23, the compositions ofExamples 17-1 to 17-5 each obtained by mixing the sample within therange of the invention exhibit good fuel-cost-saving performance, whilemaintaining high wet skid performance.

TABLE 1 Bonded Butadiene styrene 1,2-bond Amount of modifier contentcontent Tg (equivalent/active Modification ratio Mw Mooney viscositySample (wt. %) (% in BD) (° C.) Modifier lithium) (%) (10⁴) Mw/Mn (ML1 +4, 100° C.) Remarks A 28 52 −32 TGAMH *1 0.99 83 56.3 1.33 65 B 28 52−32 EPPD *2 0.90 80 50.5 1.85 63 C 28 52 −32 TGAMH 0.75 65 49.4 1.25 65D 28 52 −32 TGAMH 0.60 50 46.2 1.45 62 E 28 52 −32 SnCl₄ *3 0 0 51.51.47 65 SnCl4/Li = 0.9 F 28 52 −32 SiCl₄ *4 0 0 50.4 1.65 65 SiCl4/Li =0.9 G 28 52 −32 Not added 0 0 45.8 1.18 65 H 20 64 −34 TGAMH 0.95 8154.8 1.38 67 J 35 40 −32 TGAMH 0.95 75 51.3 1.44 65 K 28 39 −40 TGAMH0.95 78 46.7 1.46 56 L 15 45 −55 TGAMH 0.95 78 50.8 1.42 67 M 10 39 −65TGAMH 0.95 80 52.3 1.37 62 N  0 18 −92 TGAMH 0.95 70 49.8 1.40 55*1:TGAMH: tetraglycidyl-1,3-bisaminomethylcyclohexane *2:EPPD:epoxydated liquid polybutadiene *3:SnCl₄: tin tetrachloride *4:SiCl₄:silicon tetrachloride

TABLE 2 Oil Bonded Butadiene extension styrene 1,2-bond Amount ofmodifier Modification amount Oil-extended Sam- content content Tg(equivalent/ ratio Mw (parts by Mooney viscosity ple (wt. %) (% in BD)(° C.) Modifier active lithium) (%) (10⁴) Mw/Mn weight) (ML1 + 4, 100°C.) Remarks O 29 50 −33 TGAMH 0.90 72 66.5 1.77 37.5 63 P 35 36 −33SiCl₄ 0 0 75.2 1.65 37.5 85 SiCl₄/Li = 0.9 Q 35 35 −34 TGAMH 0.90 6565.6 2.48 37.5 65 R 28 52 −31 TGAMH 0.85 59 65.2 2.44 37.5 62 S 26 63−26 TGAMH 0.50 40 61.3 2.33 37.5 58 T 35 35 −34 SiCl₄ 0 0 65.2 2.55 37.566 SiCl₄/Li = 0.9 U 42 36 −24 TGAMH 0.90 70 63.8 2.33 37.5 60 V 25 65−27 TGAMH 0.95 65 61.0 2.42 37.5 55 W 42 36 −24 TGAMH 0.70 40 62.2 2.5637.5 67 Impurity-rich butadiene was used X 35 35 −34 TGAMH 0.50 35 67.12.90 37.5 64 Impurity-rich butadiene was used Y 35 35 −34 Not added 0 063.0 2.33 37.5 62 Z 33 53 −22 TGAMH 0.90 65 74.7 2.23 37.5 75 AA 35 33−36 TGAMH 4.0 75 71.3 1.95 37.5 70 AB 35 33 −36 TGAMH 1.8 78 67.1 2.3037.5 64 AC 25 65 −25 TGAMH 3.0 80 68.3 2.03 37.5 67

TABLE 3 Bonded Butadiene styrene 1,2-bond Amount of modifier contentcontent Tg (equivalent/active Modification ratio Mw Mooney viscositySample (wt. %) (% in BD) (° C.) Modifier lithium) (%) (10⁴) Mw/Mn (ML1 +4, 100° C.) Remarks BA 35 40 −32 TGAMH 2.0 83 44.6 1.55 69 BB 35 40 −32TGAMH 4.0 85 42.1 1.61 61 BC 35 40 −32 TGAMH 2.0 83 43.8 1.83 65 BD 3540 −32 TGAMH 0.95 75 52.3 1.44 65 BE 35 40 −32 SiCl₄ 0  0 53.3 1.47 68SiCl₄/Li = 1.2

TABLE 4 Bonded styrene Butadiene 1,2- Glass transition Non-oil-extendedOil extension Oil-extended content bond content point Tg MooneyViscosity amount (parts Mooney viscosity Sample Sample name (wt. %) (%in BD) (° C.) (ML1 + 4, 100° C.) by weight (ML1 + 4, 100° C.) Remarks RASBR1721 40 17 −36 — 37.5 55 Commercially (emulsion- availablepolymerization product product) RB SBR1500 23.5 17 −57 52 Commercially(emulsion- available polymerization product product) RC Asaprene 1204 2532 −56 56 — — Product of Asahi (solution- Kasei polymerization product)RD High cis BR 0 2 −108 40 — — Commercially available RE Natural rubber0 — −68 — — — Commercially RSS#1 available product RF Tafden 3335 35.533 −34 — 37.5 55 Product of Asahi (solution- Kasei polymerizationproduct) RG Tafden 2530 25 13 −70 — 37.5 40 Product of Asahi (solution-Kasei polymerization product) RH SBR1712 23.5 17 −57 — 37.5 52Commercially (emulsion available polymer) product

TABLE 5 Blending formulation S-1 S-2 S-3 S-4 S-5 S-6 S-7 S-11 S-12 S-13Rubbery polymer, total amount 100 100 100 100 100 100 100 100 100 100Aromatic oil *1 20 37.5 37.5 37.5 37.5 37.5 37.5 20 37.5 37.5 Silica *250 50 65 40 65 65 65 0 0 20 Carbon black N339 *3 5 20 5 30 5 5 5 60 7050 Silane coupling agent *4 5 5 6 4 3 1 0 0 0 2 Zinc white 2.5 2.5 2.52.5 2.5 2.5 2.5 5 5 2.5 Stearic acid 1 1 1 1 1 1 1 2 2 1 Antioxidant 3c*5 2 2 2 2 2 2 2 1 2 2 Wax 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1 1.5 Sulfur1.4 1.4 1.4 1.4 2.0 2.5 2.7 1.6 2.2 1.7 Vulcanizing accelerator CZ *61.7 1.7 1.7 1.7 1.7 1.7 1.7 1.2 1.6 1.7 Vulcanizing accelerator D *7 2 22 2 2 2 2 0 0 0 Total 192.1 224.6 225.6 223.6 223.2 221.7 220.9 192.3221.3 219.9 (Numerals of the unit in the above Table are all parts byweight) *1: “Sonic X-140”, trade name; product of Japan Energy Co., Ltd.*2: “ULTRASIL VN3”, trade name; product of Degussa *3: “Seast KH”, tradename; product of Tokai Carbon Co., Ltd. *4: “Silane coupling agent Si69”, trade name of Degussa, name of substance:bis-[3-(triethoxysilyl)-propyl]-tetrasulfide *5: Name of substance:N-isopropyl-N′-phenyl-p-phenylenediamine *6: Name of substance:N-cyclohexyl-2-benzothiazyl sulpheneamide *7: Name of substance:diphenylguanidine

TABLE 6 Time elapsed Operation First-stage kneading (B type enclosedmixer, temperature is set upon each kneading) 0 minute Charging ofrubber 0 minute and 30 seconds Charging of zinc oxide and stearic acid 1minute Charging of silica, carbon black and silane coupling agent 3minutes and 30 seconds Cleaning after ram is raised 4 minutesDischarging After discharging Discharging in portions and cooling by a10-inch roll after measurement of the temperature of the mixtureSecond-stage kneading (B type enclosed mixer, temperature is set uponeach kneading) 0 minute Charging of the first-stage kneaded mass andantioxidant 2 minutes Discharging After discharging Discharging inportions and cooling by a 10-inch roll after measurement of thetemperature of the mixture Third-stage kneading (10-inch mixing roll,set at 70° C.) 0 minute Charging of the second-stage kneaded mass 0minute 15 seconds Charging of sulfur and vulcanizing accelerator 3minutes After discharging, molding or forming

TABLE 7 Vulcanization physical properties 1st stage/2nd stage BoundProcessability Fuel-cost- kneading and rubber Viscosity of Tensilesaving Wet skid Modification Blending discharging content mixturestrength performance resistance No. Sample ratio formulation temperature[° C.]/[° C.] [wt. %] (130° C.) (MPa) (Tan δ, 50° C.) (Tan δ, 0° C.)Example 1-1 A 83 S-1 159/158 52 62 17.5 0.147 0.802 Example 1-2 B 80 S-1162/162 46 62 16.7 0.170 0.765 Example 1-3 C 65 S-1 160/160 50 64 16.70.158 0.831 Comp. Ex. 1-1 D 50 S-1 162/160 36 58 17.4 0.200 0.746 Comp.Ex. 1-2 E 0 S-1 161/162 33 41 14.5 0.214 0.738 Comp. Ex. 1-3 F 0 S-1160/160 32 60 15.1 0.210 0.745 Comp. Ex. 1-4 G 0 S-1 159/158 26 63 14.80.210 0.757

TABLE 8 Vulcanization physical properties 1st stage/2nd stage BoundProcessability Fuel-cost- Silica/Carbon kneading and rubber Viscosity ofTensile saving Wet skid Sam- Blending amounts discharging contentmixture strength performance resistance No. ple formulation [parts byweight] temperature [° C.]/[° C.] [wt. %] (130° C.) (MPa) (Tan δ, 50°C.) (Tan δ, 0° C.) Example 2-1 A S-1 50/5 159/158 52 62 17.5 0.147 0.802Comp. Ex. A S-11 0/60 164/164 32 53 17.8 0.202 0.790 2-1 Comp. Ex. D S-150/5 162/160 38 63 17.4 0.200 0.746 2-2 Comp. Ex. RB S-11 0/60 160/16128 42 23.3 0.233 0.294 2-3 Comp. Ex. RC S-11 0/60 162/162 29 40 23.30.170 0.250 2-4

TABLE 9 1st stage/2nd stage kneading and Bound Processability Physicalproperties upon vulcanization discharging rubber Viscosity of TensileFuel-cost-saving Wet skid Blending temperature content mixture strengthperformance resistance No. Sample formulation [° C.]/[° C.] [wt. %](130° C.) (MPa) (Tan δ, 50° C.) (Tan δ, 0° C.) Example 3-1 A S-1 159/15852 62 17.5 0.147 0.802 Example 3-2 H S-1 162/159 52 65 14.8 0.155 0.747Example 3-3 J S-1 160/162 48 67 18.2 0.153 0.794 Example 3-4 K S-1159/158 55 62 17.6 0.138 0.553

TABLE 10 Vulcanization physical properties 1st stage/2nd stage BoundProcessability Fuel-cost- Modification mixing and discharging rubberViscosity of Tensile saving Wet skid ratio Blending temperature contentmixture strength performance resistance No. Sample (%) formulation [°C.]/[° C.] [wt. %] (130° C.) (MPa) (Tan δ, 50° C.) (Tan δ, 0° C.)Example 4-1 O 72 S-2 162/163 58 74 20.9 0.148 0.815 Example 4-2 Q 65 S-2161/159 50 68 21.3 0.185 0.780 Comp. Ex. 4-1 P 0 S-2 162/160 53 97 21.10.188 0.775

TABLE 11 Blend 1st stage/2nd stage Vulcanization physical properties ingmixing and Bound Processability Fuel-cost- Component A-1 Component A-2for- discharging rubber Viscosity of Tensile saving Wet skid Ratio Ratiomul- temperature content blend strength performance resistance No.Sample (wt. %) Sample (wt. %) tion [° C.]/[° C.] [wt. %] (130° C.) (MPa)(Tan δ, 50° C.) (Tan δ, 0° C.) Example 5-1 A 100 — — S-2 158/158 53 4816.4 0.153 0.843 Example 5-2 A 70 RF 30 S-2 159/160 51 55 18.4 0.1630.820 Example 5-3 A 20 RF 80 S-2 161/158 48 65 20.5 0.180 0.795 Comp.Ex. A 10 RF 90 S-2 159/159 43 70 21.1 0.205 0.770 5-1 Comp. Ex. — — RF100 S-2 160/160 40 71 21.3 0.215 0.760 5-2 When The components (A-1) and(A-2) are oil-extended products, only the rubber content not includingthe amount of the extension oil is indicated by wt. %.

TABLE 12 1st stage/2nd Blend- stage mixing Vulcanization physicalproperties Component A-2 Component A-2 ing and Processability Fuel-cost-Wet skid Component A-1 (1) (2) form- discharging Viscosity of Tensilesaving resistance Ratio Ratio Ratio ula- temperature blend strengthperformance (Tan δ, No. Sample (wt. %) Sample (wt. %) Sample (wt. %)tion [° C.]/[° C.] (130° C.) (MPa) (Tan δ, 50° C.) 0° C.) Ex. 6-1 A 100 — — — — S-2 Approx. 160/ 48 16.4 0.153 0.843 approx. 160 Ex. 6-2 A 70 RB30 — — S-2 Approx. 160/ 44 21.1 0.175 0.624 approx. 160 Com. Ex. D 70 RB30 — — S-2 Approx. 160/ 42 19.3 0.203 0.602 6-1 approx. 160 Ex. 6-3 A 55P 45 — — S-2 Approx. 160/ 67 20.3 0.172 0.811 approx. 160 Ex. 6-4 A 55 R45 — — S-2 Approx. 160/ 62 19.9 0.168 0.833 approx. 160 Ex. 6-5 A 25 P75 — — S-2 Approx. 160/ 76 19.2 0.179 0.807 approx. 160 Ex. 6-6 A 20 R80 — — S-2 Approx. 160/ 64 19.9 0.177 0.812 approx. 160 Com. Ex. H 10 S90 — — S-2 Approx. 160/ 68 16.4 0.209 0.855 6-2 approx. 160 Ex. 6-7 A 50R 30 RD 20 S-2 Approx. 160/ 58 17.8 0,172 0.555 approx. 160 Ex. 6-8 A 50S 30 RD 20 S-2 Approx. 160/ 57 16.3 0.165 0.570 approx. 160 Ex. 6-9 A 40P 30 RB 30 S-2 Approx. 160/ 68 20.7 0.170 0.625 approx. 160 Ex. 6-10 A40 R 30 RB 30 S-2 Approx. 160/ 60 21.3 0.171 0.638 approx. 160 Ex. 6-11H 40 R 30 RB 30 S-2 Approx. 160/ 61 19.2 0.168 0.618 approx. 160 Ex.6-12 H 40 S 30 RB 30 S-2 Approx. 160/ 63 17.4 0.170 0.653 approx. 160Ex. 6-13 O 40 R 30 RB 30 S-2 Approx. 160/ 67 20.2 0.157 0.637 approx.160 Ex. 6-14 O 25 R 45 RB 30 S-2 Approx. 160/ 67 21.3 0.163 0.631approx. 160 Ex. 6-15 L 40 S 30 RA 30 S-2 Approx. 160/ 63 19.7 0.1630.602 approx. 160 Ex. 6-16 L 30 RA 70 — — S-2 Approx. 160/ 66 20.2 0.1680.642 approx. 160 Com. Ex. — — RA 70 RB 30 S-2 Approx. 160/ 65 21.70.214 0.582 6-3 approx. 160 Com. Ex. — — RA 80 RD 20 S-2 Approx. 160/ 6920.4 0.221 0.512 6-4 approx. 160 Com. Ex. — — P 80 RD 20 S-2 Approx.160/ 74 19.5 0.185 0.546 6-5 approx. 160 Com. Ex. — — P 100 — — S-2Approx. 160/ 92 21.1 0.188 0.775 6-6 approx. 160 When the components(A-1) and (A-2) are oil-extended products, only the rubber content notincluding the amount of the extension oil is indicated by wt. %.

TABLE 13 1st stage/2nd Vulcanization stage mixing and Processabilityphysical properties Component A-1 Component A-2 discharging Viscosity ofTensile Fuel-cost-saving Ratio Ratio Blending temperature mixturestrength performance No. Sample (wt. %) Sample (wt. %) formulation [°C.]/[° C.] (130° C.) (MPa) (Tan δ, 50° C.) Example 7-1 M 40 RE (Natural60 S-1 160/160 52 22.3 0.102 rubber) Example 7-2 N 40 RE (Natural 60 S-1161/158 48 20.3 0.097 rubber) Comp. Ex. 7-1 — — RE (Natural 100  S-1162/159 45 25.5 0.125 rubber)

TABLE 14 1st stage/2nd stage Vulcanization physical propertiesSilica/Carbon mixing and Bound Processability Fuel-cost- amountsdischarging rubber Viscosity of Tensile saving Wet skid Blending [partsby temperature content mixture strength performance resistance No.Sample formulation weight] [° C.]/[° C.] [wt. %] (130° C.) (MPa) (Tan δ,50° C.) (Tan δ, 0° C.) Example 8-1 O S-2 50/20 161/159 50 68 21.3 0.1850.780 Comp. Ex. 8-1 Q S-12  0/70 161/158 35 70 20.3 0.295 0.764 Comp.Ex. 8-2 T S-2 50/20 159/159 37 72 19.9 0.230 0.762 Comp. Ex. 8-3 X S-250/20 161/158 40 74 20.5 0.205 0.758 Comp. Ex. 8-4 RH S-12  0/70 160/16028 53 20.5 0.245 0.432

TABLE 15 1st stage/2nd Vulcanization physical properties Silica/Carbonstage mixing and Bound Processability Fuel-cost- amounts dischargingrubber Viscosity of Tensile saving Wet skid Sam- Blending [parts bytemperature content mixture strength performance resistance Re- No. pleformulation weight] [° C.]/[° C.] [wt. %] (130° C.) (MPa) (Tan δ, 50°C.) (Tan δ, 0° C.) marks Example 9-1 A S-3 65/5  158/158 53 45 17.50.142 0.852 Example 9-2 A S-2 50/20 161/159 53 48 16.4 0.153 0.843Example 9-3 A S-4 40/30 159/159 48 48 18.3 0.185 0.813 Comp. Ex. A S-1320/50 160/161 40 51 18.4 0.222 0.805 9-1 Comp. Ex. A S-12  0/70 161/15833 50 18.5 0.242 0.800 9-2

TABLE 16 1st stage/2nd stage Vulcanization physical properties mixingand Bound Processability Fuel-cost- discharging rubber Viscosity ofTensile saving Wet skid Blending temperature content mixture strengthperformance resistance No. Sample formulation [° C.]/[° C.] [wt. %](130° C.) (MPa) (Tan δ, 50° C.) (Tan δ, 0° C.) Example 10-1 U S-2160/160 45 70 22.6 0.227 1.025 Example 10-2 V S-2 161/160 48 63 18.20.212 0.975 Example 10-3 Z S-2 161/158 51 68 20.2 0.202 0.995 Comp. Ex.W S-2 159/161 32 67 16.7 0.258 0.955 10-1

TABLE 17 1st stage/2nd stage mixing Vulcanization physical propertiesComponent Component Component and Processability Fuel-cost- Wet skid A-1A-2 (1) A-2 (2) discharging Viscosity of Tensile saving resistance Sam-Ratio Sam- Ratio Sam- Ratio Blending temperature mixture strengthperformance (Tan δ, No. ple (wt. %) ple (wt. %) ple (wt. %) formulation[° C.]/[° C.] (130° C.) (MPa) (Tan δ, 50° C.) 0° C.) Ex. 11-1 V 70 RD 30— — S-3 158/158 65 15.9 0.142 0.465 Ex. 11-2 V 35 RD 30 RA 35 S-3160/160 68 18.8 0.154 0.480 Ex. 11-3 V 58 RD 22 RE 20 S-3 158/158 6016.5 0.144 0.454 Ex. 11-4 U 55 RD 45 — — S-3 159/161 71 19.6 0.157 0.524Ex. 11-5 U 35 RD 30 RA 35 S-3 159/161 72 20.3 0.161 0.504 Com. Ex. — —RD 30 RA 70 S-3 158/158 74 21.9 0.185 0.455 11-1 When the components(A-1) and (A-2) are oil-extended products, only the rubber content notincluding the amount of the extension oil is indicated by wt. %.

TABLE 18 1st stage/2nd stage mixing Vulcanization physical propertiesComponent Component Component and Processability Fuel-cost- Wet skid A-1A-2 (1) A-2 (2) discharging Viscosity of Tensile saving resistance Sam-Ratio Sam- Ratio Sam- Ratio Blending temperature mixture strengthperformance (Tan δ, No. ple (wt. %) ple (wt. %) ple (wt. %) formulation[° C.]/[° C.] (130° C.) (MPa) (Tan δ, 50° C.) 0° C.) Ex. 12-1 Q 40 RF 20RH 40 S-5 161/159 72 21.4 0.180 0.635 Ex. 12-2 Q 75 RG 25 — — S-5160/160 65 20.8 0.186 0.620 Ex. 12-3 Q 50 RA 25 RG 25 S-5 161/160 7022.5 0.190 0.638 Ex. 12-4 Q 58 RH 42 — — S-5 159/158 69 21.2 0.185 0.632Ex. 12-5 Q 58 RC 42 — — S-5 159/158 63 20.3 0.180 0.618 Ex. 12-6 Q 40 RA30 RH 30 S-5 161/160 72 22.3 0.192 0.642 Com. Ex. Q 10 RA 50 RH 40 S-5160/158 70 18.4 0.221 0.611 12-1 Com. Ex. — — RA 60 RH 40 S-5 159/157 7220.1 0.213 0.603 12-2 Com. Ex. — — RA 60 RC 40 S-5 156/156 68 19.5 0.2220.615 12-3 When the components (A-1) and (A-2) are oil-extendedproducts, only the rubber content not including the amount of theextension oil is indicated by wt. %.

TABLE 19 Conditions Vulcanization physical properties 1st stage/2ndstage Bound Processability Fuel-cost- Heating loss mixing anddischarging rubber Viscosity of Tensile saving Wet skid Sam- Blending ofsilica (Mc) temperature content mixture strength performance resistanceNo. ple formulation [wt. %] [° C.]/[° C.] [wt. %] (130° C.) (MPa) (Tanδ, 50° C.) (Tan δ, 0° C.) Example 13-1 J S-2 2.2 141/138 44 42 21.70.153 0.911 Example 13-2 J S-2 2.2 150/150 48 50 20.8 0.148 0.922Example 13-3 J S-2 1.1 141/139 41 43 22.0 0.152 0.887 Example 13-4 J S-24.8 150/155 57 48 19.1 0.132 0.966 Example 13-5 J S-2 6.5 169/169 59 5219.3 0.130 0.982 Example 13-6 J S-2 6.5 175/170 64 58 17.9 0.112 1.025Example 13-7 J S-2 8.2 167/168 55 50 19.8 0.134 0.968 Example 13-8 J S-24.8 142/140 38 38 19.4 0.178 0.838

TABLE 20 Conditions Amount of 1st stage/2nd Vulcanization physicalproperties organosilane stage mixing and Bound Processability Fuel-cost-coupling agent discharging rubber Viscosity of 300% Tensile saving Wetskid Sam- Blending (parts by temperature content mixture Modulusstrength performance resistance No. ple formulation weight) [° C.]/[°C.] [wt. %] (130° C.) (Mpa) (MPa) (Tan δ, 50° C.) (Tan δ, 0° C.) Ex.14-1 J S-5 3 160/162 54 48 11.0 19.7 0.127 0.945 Ex. 14-2 J S-6 1161/161 57 50 11.8 19.1 0.128 0.957 Ex. 14-3 J S-7 0 160/160 48 62 10.216.5 0.165 0.900 Ex. 14-4 Q S-5 3 160/161 60 72 12.9 21.5 0.136 0.895Ex. 14-5 Q S-6 1 158/161 61 76 14.0 21.3 0.134 0.887 Ex. 14-6 Q S-3 6160/160 57 71 12.5 22.2 0.170 0.800 Com. Ex. F S-5 3 159/160 30 55 10.117.0 0.198 0.711 14-1 Com. Ex. F S-6 1 162/162 27 60 10.3 16.9 0.2050.702 14-2 Com. Ex. F S-3 6 158/158 33 42  8.9 17.7 0.195 0.715 14-3

TABLE 21 Conditions 1st stage/2nd stage Vulcanization physicalproperties mixing and Bound Processability Fuel-cost- discharging rubberViscosity of 300% Tensile saving Wet skid Blending temperature contentmixture Modulus strength performance resistance No. Sample formulation[° C.]/[° C.] [wt. %] (130° C.) (Mpa) (MPa) (Tan δ, 50° C.) (Tan δ, 0°C.) Example 15-1 BA S-3 158/159 40 41 9.8 20.3 0.121 0.925 Example 15-2BA S-5 158/159 46 45 12.2 19.6 0.113 0.951 Example 15-3 BB S-3 160/16043 44 10.2 20.0 0.118 0.930 Example 15-4 BB S-5 160/161 50 47 12.4 19.90.110 0.968 Example 15-5 BC S-3 158/158 42 42 11.4 19.8 0.117 0.953Example 15-6 BD S-5 160/160 54 43 11.0 19.7 0.127 0.945 Comp. Ex. 15-1BE S-3 158/158 32 42 8.9 17.7 0.205 0.705 Comp. Ex. 15-2 RB S-3 158/16029 45 7.9 20.3 0.216 0.380

TABLE 22 Conditions 1st stage/2nd stage Vulcanization physicalproperties mixing and Bound Processability Fuel-cost- discharging rubberViscosity of 300% Tensile saving Wet skid Blending temperature contentmixture Modulus strength performance resistance No. Sample formulation[° C.]/[° C.] [wt. %] (130° C.) (MPa) (MPa) (Tan δ, 50° C.) (Tan δ, 0°C.) Example 16-1 AA S-5 161/162 55 64 12.4 21.8 0.126 0.904 Example 16-2AB S-5 159/159 52 72 12.1 21.3 0.135 0.864 Example 16-3 AC S-5 161/16154 70 13.5 19.3 0.140 1.042 Com. Ex. 16-1 T S-5 159/159 42 68 11.2 20.20.200 0.820 Com. Ex. 16-2 Y S-5 160/160 40 65 10.9 19.7 0.202 0.810Example 16-4 AA/RD = S-5 161/162 52 59 9.9 22.9 0.142 0.559 80/20Example 16-5 AB/RD = S-5 159/162 51 61 9.8 21.5 0.140 0.562 80/20 Com.Ex. 16-3 X/RD = S-5 158/160 43 60 9.2 19.5 0.175 0.540 80/20 Example16-5 BA/RA = S-5 159/161 54 60 10.3 22.2 0.138 0.850 40/60

TABLE 23 Conditions 1st stage/2nd Vulcanization physical propertiesComponent Component stage mixing Bound Processability 300% Fuel-cost-(A-1) (1) (A-1) (2) and discharging rubber Viscosity of Mod- Tensilesaving Wet skid Sam- Ratio Sam- Ratio Blending temperature contentmixture ulus strength performance resistance No. ple (wt. %) ple (wt. %)formulation [° C.]/[° C.] [wt. %] (130° C.) (MPa) (MPa) (Tan δ, 50° C.)(Tan δ, 0° C.) Ex. A 60 Q 40 S-3 160/159 53 55 12.5 18.5 0.140 0.85217-1 Ex. A 60 AA 40 S-3 160/159 55 55 12.8 19.7 0.115 0.883 17-2 Ex. A30 AA 70 S-3 160/160 55 65 13.5 20.9 0.114 0.884 17-3 Ex. BA 30 Q 70 S-3160/161 52 64 13.2 20.4 0.128 0.895 17-4 Ex. BA 30 AA 70 S-3 159/158 5867 13.3 21.2 0.118 0.905 17-5

INDUSTRIAL APPLICABILITY

Provided is a vulcanized rubber composition for tire tread having goodstrength properties, processability, fuel-cost-saving performance andgripping performance by using a styrene-butadiene rubber having aspecific structure of the invention in accordance with a specificblending formulation containing a reinforcing silica filler. Theinvention makes it possible to reduce the amount of a silane couplingagent necessary for obtaining a silica-containing composition. Thisvulcanized rubber composition for tires is useful as an automobile tirematerial requiring fuel-cost-saving performance.

1. A process for producing a rubbery polymer having a high modificationratio through reaction of a diene polymer having an active end and amodifier, comprising the steps of: reacting impurities contained in amonomer and a solvent with an organic metal compound to inactivate theimpurities; feeding the monomer and solvent into a polymerizationreactor; and carrying out polymerization.
 2. The process according toclaim 1 wherein an amount of all the impurities in the monomer andsolvent to be fed to the polymerization reactor is reduced to less than0.40 equivalent based on an initiator to be fed to the polymerizationreactor, and the rubber polymer obtained contains a modified componentin an amount exceeding 60 wt. %.
 3. The process according to claim 1,wherein the modifier is a polyfunctional compound having at least twoepoxy groups in its molecule.
 4. The process according to claim 2,wherein the modifier is a polyfunctional compound having at least twoepoxy groups in its molecule.
 5. The process according to claim 1,wherein the modifier is a polyfunctional compound having at least twoepoxy groups and at least one nitrogen atom in its molecule.
 6. Theprocess according to claim 2, wherein the modifier is a polyfunctionalcompound having at least two epoxy groups and at least one nitrogen atomin its molecule.
 7. The process according to claim 1, wherein themodifier is represented by the following formula:

wherein, R¹ and R² each independently represents a C₁₋₁₀ hydrocarbongroup or a C₁₋₁₀ hydrocarbon group having an ether or a tertiary amine,R³ and R⁴ each independently represents hydrogen, a C₁₋₂₀ hydrocarbongroup or a C₁₋₂₀ hydrocarbon group having an ether or tertiary amine, R⁵represents a C₁₋₁₂ hydrocarbon group or a C₁₋₁₂ hydrocarbon group havingat least one group selected from ethers, tertiary amines, epoxy,carbonyl and halogens, and n stands for 1 to
 6. 8. The process accordingto claim 2, wherein the modifier is represented by the followingformula:

wherein, R¹ and R² each independently represents a C₁₋₁₀ hydrocarbongroup or a C₁₋₁₀ hydrocarbon group having an ether or a tertiary amine,R³ and R⁴ each independently represents hydrogen, a C₁₋₂₀ hydrocarbongroup or a C₁₋₂₀ hydrocarbon group having an ether or tertiary amine, R⁵represents a C₁₋₁₂ hydrocarbon group or a C₁₋₁₂ hydrocarbon group havingat least one group selected from ethers, tertiary amines, epoxy,carbonyl and halogens, and n stands for 1 to 6.